This invention relates to the field of optics and lasers, and more specifically to a method and apparatus including multi-compositional glass substrates and related devices and optical waveguides on a glass substrate.
The telecommunications industry commonly uses optical fibers to transmit large amounts of data in a short time. One common light source for optical-fiber communications systems is a laser formed using erbium-doped glass. One such system uses erbium-doped glass fibers to form a laser that emits at a wavelength of about 1.536 micrometer and is pumped by an infrared source operating at a wavelength of about 0.98 micrometer. One method usable for forming waveguides in a substrate is described in U.S. Pat. No. 5,080,503 issued Jan. 14, 1992 to Najafi et al., which is hereby incorporated by reference. A phosphate glass useful in lasers is described in U.S. Pat. No. 5,334,559 issued Aug. 2, 1994 to Joseph S. Hayden, which is also hereby incorporated by reference. An integrated optic laser is described in U.S. Pat. No. 5,491,708 issued Feb. 13, 1996 to Malone et al., which is also hereby incorporated by reference.
To increase signal-carrying bandwidth, an optical fiber can carry a plurality of different wavelengths (i.e., colors), wherein each wavelength is modulated (e.g., using amplitude modulation) with a different signal stream. Dense wavelength-division multiplexing (DWDM) is the name for one such scheme wherein each signal stream is modulated on a carrier wavelength that is close to, but slightly different than, the neighboring wavelengths. For example, the carrier wavelengths can be chosen in the infrared at, say, 1536 nm, 1536.8 nm, 1537.6 nm, etc., for a wavelength spacing of 0.8 nm per channel. Many such wavelengths/channels can be combined and transmitted on a single optical fiber. Since photons have extraordinarily low or no interaction with one another, these channels are transmitted with no crosstalk or other interchannel interference. Further, a broadband light amplifier can be used to simultaneously amplify all the colors/channels by equal amounts, also without introducing crosstalk. The challenge, thus, is to be able to separate the channels (i.e., to split off each channel""s color without also getting interfering light signals from adjacent channels"" colors).
It is desirable to be able, at, for example, a building in downtown Minneapolis, to extract one channel from the plurality of optical channels of data carried on a single optical fiber, e.g., to extract a first data stream that is modulated on the 1536.8 nm channel from all the other channels on some single optical fiber, and to insert in its place a second data stream that is modulated on the 1536.8 nm channel. The remaining channels being transmitted on the optical fiber should be undisturbed. This allows data that has a destination in that building to be separated and delivered into that building, and for other data in the second data stream to be sourced from that building and sent elsewhere.
There is a need in the art for an integrated optical system, including one or more high-powered lasers along with routing and other components, that can be inexpensively mass-produced. The system should be highly reproducible, accurate, and stable. There is further a need to having improved delivery of pump light to the active waveguides. There is further a need for improved add-drop devices that permit extraction of a first signal stream at a first wavelength from a plurality of other signal wavelengths, and insertion of a second signal stream modulated onto a laser carrier of the first wavelength.
The present invention is embodied by a laser, amplifier, other optical or combined component that includes a glass substrate, in some or all portions possibly doped with one or more optically active lanthanide species, and having a plurality of waveguides defined by channels within the substrate.
One aspect of the present invention provides an integrated photonic apparatus that includes a glass substrate having a major surface, wherein the glass substrate includes a plurality of regions, each region having a different index of refraction, including a first region having a first index of refraction and a second region having a second index of refraction lower than the first index of refraction, and a first waveguide formed along the major surface of the substrate, wherein the first waveguide has a higher index of refraction than an intrinsic index of refraction of adjacent portions of the substrate, and wherein the first waveguide passes through the first region and through the second region of the glass substrate.
In some embodiments, the first region includes a dopant including an optically active species, wherein the first region acts to substantially confine a pump light. In some embodiments, the higher index of refraction of the first region allows pump light to enter the first region but not escape to the second region.
Another aspect of the present invention provides an integrated photonic apparatus that includes a glass substrate having a major surface, wherein the glass substrate includes a plurality of regions, each region having a different index of refraction, including a first region having a first index of refraction and a second region having a second index of refraction lower than the first index of refraction, the first region forming a first waveguide for constraining a pump light, and a second waveguide formed along the major surface of the substrate, wherein the second waveguide has a higher index of refraction than an intrinsic index of refraction of adjacent portions of the substrate, and wherein the second waveguide passes through the first region and through the second region of the glass substrate, and wherein the pump light enters the second waveguide along its side in the first waveguide.
Another aspect of the present invention provides apparatus and methods for stabilizing and/or flattening gain curves. For example, a tuned grating to stabilize the input pump laser light, to flatten output gain curve, or both.
One embodiment includes an integrated photonic apparatus that has a glass substrate having a major surface, an input signal waveguide formed along the major surface of the substrate, wherein the input signal waveguide has a higher index of refraction than an index of refraction of adjacent portions of the substrate, an input pump waveguide formed along the major surface of the substrate, wherein the pump waveguide has a higher index of refraction than an index of refraction of adjacent portions of the substrate, an output pump waveguide, optically coupled to the input signal waveguide and to the pump waveguide, and formed along the major surface of the substrate, wherein the pump waveguide has a higher index of refraction than an index of refraction of adjacent portions of the substrate, and a first pump-stabilizing grating formed on the pump waveguide, wherein the first grating is transparent a first wavelength and is dispersive to a plurality of other wavelengths, such that the first wavelength is passed to the output waveguide and the plurality of other wavelengths are attenuated.
Yet another aspect of the present invention provides an integrated photonic apparatus including a glass substrate having a major surface, the substrate including at least a portion having one or more active optical species, an input signal waveguide formed along the major surface of the substrate, wherein the input signal waveguide has a higher index of refraction than an index of refraction of adjacent portions of the substrate, an input pump waveguide formed along the major surface of the substrate, wherein the pump waveguide has a higher index of refraction than an index of refraction of adjacent portions of the substrate, an output pump waveguide, optically coupled to the input signal waveguide and to the pump waveguide, and formed along the major surface of the substrate, wherein the pump waveguide has a higher index of refraction than an index of refraction of adjacent portions of the substrate, and a first output-flattening grating formed on the output waveguide, wherein the first output-flattening grating has a wavelength-transfer function that is complementary to a gain curve of the active species of the substrate in order to flatten a gain curve of the apparatus.
The present invention also provides apparatus and methods for adding and/or dropping one or more optical wavelengths from a light signal having a plurality of wavelengths. For example, selectable gratings to get a tunable/selectable drop (peel-off) wavelength, an add waveguide that is run in an undoped region running parallel to the active drop section, and/or an add/drop peel-off section surrounded with a confined active region. Some embodiments selectively pump waveguides in a lossy gain region to activate add/drop attenuation/amplification functions, such that specific waveguides are activated. In some such embodiments, this is combined with an undoped region fused to active region, wherein pump light is launched into undoped waveguides that route activation light to selected doped waveguides.
Some embodiments include an integrated photonic apparatus that has a glass substrate having a major surface, an input signal waveguide formed along the major surface of the substrate, wherein the input waveguide has a higher index of refraction than an index of refraction of adjacent portions of the substrate, an output signal waveguide, optically coupled to the input waveguide, and formed along the major surface of the substrate, wherein the output waveguide has a higher index of refraction than an index of refraction of adjacent portions of the substrate, a drop signal waveguide, optically coupled to the input waveguide, and formed along the major surface of the substrate, wherein the drop waveguide has a higher index of refraction than an index of refraction of adjacent portions of the substrate, and a first grating formed on the output waveguide, wherein the first grating reflects a first wavelength and is transparent to a plurality of other wavelengths, such that the first wavelength is passed to the drop waveguide and the plurality of other wavelengths is passed through to an exit interface of the output waveguide.
Some such embodiments further include a second grating formed on the output waveguide, wherein the first and second gratings are electrically activatable, and wherein the first grating when activated reflects a first wavelength and is transparent to a plurality of other wavelengths including a second wavelength, wherein the second grating when activated reflects the second wavelength and is transparent to a plurality of other wavelengths including the first wavelength, such that when the first grating is activated and the second grating is deactivated the first wavelength is passed to the drop waveguide and the second wavelength is passed through to the exit interface of the output waveguide, and when the second grating is activated and the first grating is deactivated the second wavelength is passed to the drop waveguide and the first wavelength is passed through to the exit interface of the output waveguide.
Some embodiments further include an add signal waveguide, optically coupled to the output waveguide, and formed along the major surface of the substrate, wherein the add waveguide has a higher index of refraction than an index of refraction of adjacent portions of the substrate, and wherein the first grating reflects a first wavelength and is transparent to a plurality of other wavelengths, wherein a third wavelength is launched into the add waveguide, such that the first wavelength is passed to the drop waveguide and the plurality of other wavelengths and the third wavelength are passed through to an exit interface of the output waveguide.
Some embodiments further include an add signal waveguide, optically coupled to the output waveguide, and formed along the major surface of the substrate, wherein the add waveguide has a higher index of refraction than an index of refraction of adjacent portions of the substrate, and wherein the first grating reflects a first wavelength and is transparent to a plurality of other wavelengths, wherein a third wavelength is launched into the add waveguide, such that the first wavelength is passed to the drop waveguide and the plurality of other wavelengths and the third wavelength are passed through to an exit interface of the output waveguide.